The invention is generally related to the inspection of welds and, more particularly, to the ultrasonic inspection of pipe-to-fitting welds where there is limited clearance.
In the offshore drilling industry for producing oil and natural gas, production, delivery, and various processes on the offshore rigs and platforms require the use of a variety of pipes and fittings that must be welded together. Safety requirements require that the welds be inspected for the detection and repair of weld defects.
Previously, radiography was the primary method of inspection for process piping welds with limited clearance for inspection. The non-destructive inspection of carbon steel pipe-to-fitting joints using the alternative method of ultrasonic inspection is preferred.
A limitation of ultrasonic inspection is that ultrasonic transducers must be able to be positioned on the parent material adjacent to the weld so as to satisfactorily inspect the full volume of the weld. As seen in FIG. 1, using phased array ultrasonic transducers 40 to inspect the weld 42 between straight sections of pipe 44 or curved sections of pipe presents no issues as long as the radius of the curvature at a pipe bend is not so small as to prevent proper positioning of the transducers. Typically, about 110 mm of scanning access is required on both sides of the weld for an adequate inspection of the full weld volume.
As seen in FIGS. 2 and 3, production and process piping requires that fittings 43 for valves, controls, gauges, manifolds, or curved pipes, etc. be included in the pipes 44. Ultrasonic inspection of pipe-to-fitting welds 42 can present a challenge due to the smaller radius of curvature at the fitting and restricted scanning access on the fitting side of the weld. An example is indicated as area 46 in FIG. 2, which can make it difficult or impossible to inspect the full volume of the weld with previous transducer arrangements. A result is that a blind area 48 such as that indicated in FIG. 3 may exist where the ultrasonic transducers are not capable of being properly positioned for inspecting the full area of the weld 42.
Phased array ultrasonic inspection of pipe-to-fitting welds from the pipe side of the weld typically does not detect defects on the fitting side of the weld. It can be seen from the above that there is a need for an improved ultrasonic transducer arrangement for inspecting the fitting side of pipe-to-fitting welds.